Download - The b -delayed deuteron-decay of 6 He
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The -delayed deuteron-decayof 6He
J. Ponsaers, R. Raabe, F. Aksouh, D. Smirnov, I. Mukha, A. Sanchez, M. Huyse, P. Van Duppen, C.
Angulo, O. Ivanov, J.C. Thomas
1. Introduction2. Experiment3. Analysis4. Conclusion
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Discovered in 1985: high interaction cross section.[1]Extended matter distribution.6He is a Borromean system of + n + n
6He
E
r
Usual probability density of a neutron
E
r
Probability density of a halo neutron
6He = 2n-halo-nucleus
[1] : Tanihata I. et al. ; Phys. Rev. Letters (1985)
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II
I
Discovered in 1985: high interaction cross section.[1]Extended matter distribution.6He is a Borromean system of + n + n
6He
E
r
Usual probability density of a neutron
E
r
Probability density of a halo neutron
6He = 2n-halo-nucleus
[1] : Tanihata I. et al. ; Phys. Rev. Letters (1985)
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II
I
Discovered in 1985: high interaction cross section.[1]Extended matter distribution.6He is a Borromean system of + n + n
6He
E
r
Usual probability density of a neutron
E
r
Probability density of a halo neutron
6He = 2n-halo-nucleus
[1] : Tanihata I. et al. ; Phys. Rev. Letters (1985)
We want to measure: • Branching ratio of the decay channel II: very small (~10-6) very difficult• Energy spectrum of the decay particles E+d
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Information provided by the deuteron-branch of 6He
1. High branching ratio dineutron correlation
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Information provided by the deuteron-branch of 6He
1. High branching ratio dineutron correlation2. Low branching ratio cigar correlation
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Information provided by the deuteron-branch of 6He
Reference Branching ratio (10-6)
E d >E 0
Cutoff energy E 0 (lab), keV
[1] Isolde (1990) [2] Isolde (1993) Triumf (1994) [3] Triumf (2002) [4] Two Center Cluster Model [5] Three-Body (,n,n) Model (hypersph. co.) [6] Dynamical Microscopic Cluster Model
2.8(5) 7.6(6) 1.8(9)
2.6(1.3)
200
30-40 3.1
250 350 350
0
250
350
[1] K. Riisager et al., Phys. Lett. B 235(1990)30[2] M. J. G. Borge et al., Nucl. Phys. A 560(1993)664[3] D. Anthony et al. Phys., Rev. C 65(2002)034310
[ 4] P. Descouvement and C. Leclercq- Willain, J. Phys. G 18(1992)L99[5] M. V. Zhukov et al., Phys. Rev. C 47(1993)2937[6] A. Csoto and D. Baye, Phys. Rev. C 49(1994)818
[6] suggests that we need a detailed description of thewave functions to explain the decay.
1. High branching ratio dineutron correlation 2. Low branching ratio cigar correlation
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The methodProblems in previous experiments:•High threshold energies for deuterons •Large uncertainties (difficult to normalize)
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The methodProblems in previous experiments:•High threshold energies for deuterons•Large uncertainties (difficult to normalize)
New method: 6He implantation in DSSSD(Double Sided Silicon Strip Detector)This can count implantations AND + d decays
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The method
DSSSD divided into 48 strips x 48 strips = 2304 pixelsSmall pixel size (300m)
•Get the energy drop of -particles below the spectrum of the br.ratio•No problem for + d detection
Problems in previous experiments:•High threshold energies for deuterons•Large uncertainties (difficult to normalize)
New method: 6He implantation in DSSSD(Double Sided Silicon Strip Detector)This can count implantations AND + d decays
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The experiment
Beam on (1s): implantation and detection of 6He nuclei number of implantations counted absolute normalization for br.rat. very accurate
Beam off (2s): detection of decay of 6He nuclei caught inside the detector
6He nuclei at 8 MeV periodically implanted into DSSSD detector.
Experiment: performed at CRC, Louvain-la-Neuve, Belgium
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Analysis
1. -peak2. 6He implants3. partial E-collection
Beam on + off E (keV)
21
(Num
ber
of e
vent
s)/(
10ke
V)
3
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Beam off E (keV)
(Num
ber
of e
vent
s)/(
10ke
V)
1
Analysis
1
Time spectrum exp. fit 1: T1/2 = 806.0ms
1. -peak2. 6He implants3. partial E-collection4. + d events
Beam on + off E (keV)
21
(Num
ber
of e
vent
s)/(
10ke
V)
3
4
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Beam off E (keV)
(Num
ber
of e
vent
s)/(
10ke
V)
1
Analysis
1
Time spectrum exp. fit 1: T1/2 = 806.0ms
1. -peak2. 6He implants3. partial E-collection4. + d events
Beam on + off E (keV)
21
(Num
ber
of e
vent
s)/(
10ke
V)
3
4
Suspicious: background much higher than expected!
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Beam off E (keV)
(Num
ber
of e
vent
s)/(
10ke
V)
1
Analysis
Beam off E (keV)
1
4
1
4
Time spectrum exp. fit 1: T1/2 = 806.0ms2: T1/2 = 1102ms
1. -peak2. 6He implants3. partial E-collection4. + d events
Beam on + off E (keV)
21
(Num
ber
of e
vent
s)/(
10ke
V)
(Num
ber
of e
vent
s)/(
10ke
V)
Suspicious: background much higher than expected!
3
4
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Beam off E (keV)
(Num
ber
of e
vent
s)/(
10ke
V)
1
Beam off E (keV)
1
4
1
4
Time spectrum exp. fit 1: T1/2 = 806.0ms2: T1/2 = 1102ms
1. -peak2. 6He implants3. partial E-collection4. + d events
Beam on + off E (keV)
21
(Num
ber
of e
vent
s)/(
10ke
V)
(Num
ber
of e
vent
s)/(
10ke
V)
Suspicious: background much higher than expected!
2.New fit:
162 ± 69 background events 425 + d events
3
4
Analysis
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•Total branching ratio: W = (2.03 ± 0.35) x 10-6
•Corresponds with the value from microscopic description
•Large uncertainty from background events.
•No reliable energy spectrum of + d because we don’t know the energy spectrum of the background.
Conclusion and outlook
•New measurement on 6He in Louvain-la-Neuve
•Same experiment on 11Li at TRIUMF